JPH04187776A - Method for etching polyimide resin - Google Patents

Abstract

PURPOSE:To improve the adhesion of the surface of a copper-polyimide substrate to a resist and to enhance etching accuracy by washing the surface of the substrate with sulfuric acid having a prescribed concn., forming an etching resist layer and carrying out etching. CONSTITUTION:The surface of polyimide resin is electroless-plated or further electroplated and a copper-polyimide substrate is formed. The surface of this substrate is washed with sulfuric acid having 20wt.% or higher concn. to remove impurities sticking to the surface and to improve the adhesion to an etching resist layer formed on the surface. The etching resist layer is then formed on the washed surface and the part of the substrate not covered with the layer is etched.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention forms a copper coating on the surface of a polyimide resin by electroless plating or subsequent electrolytic plating,
The present invention then relates to a method of forming a circuit using a copper polyimide substrate obtained by subjecting it to heat treatment.

[Prior Art] Polyimide resin has excellent heat resistance and mechanical, electrical, and chemical properties comparable to other plastic materials, so it is often used as an insulating material for electrical equipment. There is. For example, printed wiring boards (PWB), flexible printed circuits (FPC), tape automatic bonding (TAB) mounting, etc. are obtained by processing a copper polyimide substrate obtained by forming a copper coating on this polyimide resin.

Conventionally, copper polyimide substrates, which are the materials for such PWBs and FPCSTABs, have generally been manufactured using a lamination method in which polyimide resin and copper foil are bonded together using an adhesive.

However, in the substrate obtained by this lamination method, impurities such as chlorine ions and sulfate ions are adsorbed to the adhesive layer existing at the interface between the copper coating and the polyimide resin during the etching process of the copper coating and the peeling process of the photoresist. If the distance between the circuits formed on the substrate is particularly narrow, problems such as poor insulation may occur. In order to overcome these drawbacks, a method has been proposed in which a metal layer is directly formed on the surface of a polyimide resin without intervening an adhesive or the like to obtain a copper polyimide substrate. For example, a copper polyimide substrate is obtained by etching and activating the polyimide resin surface, applying a catalyst, then electroless plating and, if necessary, continuing electrolytic plating. The substrate is heat treated at 120°C or higher to improve adhesion and chemical resistance.

[Problems to be Solved by the Invention] The copper polyimide substrate obtained by the above method not only maintains high adhesion between the copper coating and the polyimide resin even in a high temperature environment, but also has excellent chemical resistance, so it is suitable for PWB.
It is suitable as a material for electronic components such as SFPC and TAB.

By the way, a general process for manufacturing a TAB, which allows for the highest density among the above-mentioned electronic components, includes a process of forming holes such as sprocket holes and device holes. This process involves forming a resist layer on the polyimide resin surface of a copper polyimide substrate, exposing it to light using a desired mask, developing and dissolving it to expose a desired part of the polyimide resin, and removing this part by etching. It is something. When the polyimide resin of the copper polyimide substrate obtained by the above method is etched using this method, unlike the conventional method, the part covered with the polyimide resin etching resist layer is etched, making it impossible to obtain holes of the desired shape. A new problem has arisen.

The object of the present invention is to perform electroless plating on a polyimide resin, and if necessary, to form a copper film by electrolytic plating, and then to perform heat treatment to dissolve and remove the polyimide resin portion of the copper polyimide substrate. An object of the present invention is to provide a method for etching a polyimide resin, which makes it possible to dissolve only a desired portion of the polyimide resin.

[Means for Solving the Problems] As a result of various studies in order to solve the above problems, the present inventors found that because the adhesion between the polyimide resin surface and the etching resist was insufficient, the solution of the polyimide resin did not interact with the polyimide resin. It was discovered that the polyimide resin penetrates into the interface of the etching resist, and the polyimide resin begins to dissolve from the interface, and as a result, part of the polyimide resin that is covered with the etching resist layer and should not be dissolved is also dissolved. This led to the present invention.

That is, the method of the present invention for solving the above problems is based on a copper polyimide substrate obtained by electroless plating on a polyimide resin, followed by electrolytic plating if necessary to form a copper coating, and then heat treatment. In the method of dissolving and removing the polyimide resin portion, after cleaning the surface of the polyimide resin with sulfuric acid having a concentration of 20% by weight or more, an etching resist layer is formed, and the portions of the polyimide resin not covered by the etching resist layer are etched. and remove it.

[Function] Electroless plating is performed on the polyimide resin, followed by electrolytic plating if necessary to form a copper film, and then heat treatment is performed to form a copper film. The reason for the lack of adhesion is thought to be that impurities adhere to the polyimide resin surface when the substrate is heat-treated, and these impurities cannot be completely removed by normal cleaning methods and remain on the polyimide resin surface. .

Although sufficient knowledge has not been obtained regarding the mechanism by which the impurities are generated, it is thought that substances generated from within the polyimide resin when the substrate was heat-treated adhered firmly to the surface of the polyimide resin.

The present invention improves the adhesion between the polyimide resin surface and the etching resist by cleaning the polyimide resin surface with sulfuric acid before applying the etching resist to the substrate, but this is the result of various studies on cleaning methods for the polyimide resin surface. This is the knowledge obtained and is considered to be the most effective cleaning method for removing the impurities.

In the present invention, sulfuric acid with a concentration of 20% by weight or more is used.

If the sulfuric acid concentration is 20% by weight or less, sufficient adhesion between the polyimide resin surface of the resulting substrate and the resist will not be obtained even if heated during cleaning, and the polyimide resin will not be dissolved or removed when the polyimide resin is removed. During the process, the polyimide resin part covered with the stitching resist is also partially dissolved.

The cleaning time and the temperature of the sulfuric acid used in the present invention vary depending on the sulfuric acid concentration, the heat treatment conditions of the substrate, etc., and cannot be determined unconditionally. Therefore, during the treatment, it is necessary to determine appropriate conditions in advance through preliminary experiments to avoid insufficient cleaning.

Further, it is not necessary to use a special etching resist for polyimide resin, as long as it is resistant to the solution of polyimide resin, and the effects of the present invention can be sufficiently obtained under the conditions for forming the resist using conventional methods.

[Example 1] After forming a copper plating film with a thickness of 1.5 μm on an NPI-50 type polyimide film manufactured by Kanekabuchi Chemical Industry Co., Ltd. by electroless copper plating method, the substrate was placed in a vacuum heating furnace. Temperature increase rate 10°C/at vacuum level 10”-’ torr
After heating at 400°C for 1 hour, the mixture was cooled to room temperature. The obtained substrate was immersed in an aqueous solution containing 50% by weight of sulfuric acid at 25° C. for 2 minutes, thoroughly washed with water, and then dried. Thereafter, a photoresist PMERHC-600 manufactured by Tokyo Ohka Kogyo Co., Ltd. was uniformly applied to a thickness of 40 μm on the copper plating film of the substrate, and dried at 70° C. for 30 minutes. Thereafter, a mixture of photoresist FSR-S manufactured by Fuji Pharmaceutical Co., Ltd. and diluent FSR-T in an equal volume ratio was uniformly applied to a thickness of 10 μm on the polyimide resin surface of the substrate and dried at 70° C. for 30 minutes. The lead width is 70 μm and the lead spacing is 60 μm at the inner lead part on the PMER side of the obtained substrate.
Masking was applied to form leads of 10100 O/cm" and 100 m" for each photoresist layer, while masking was applied to form device holes and sprocket holes on the FSR side.
After irradiation with ultraviolet rays of J/cm", development was performed. After that, copper was electroplated to a thickness of 35 μm on the exposed electroless copper plating film, and the PMER was peeled off. After that, the electroless copper plating film was electroplated. Dissolution and removal was performed using the copper plating film as a mask.

Thereafter, a photoresist FSR-S manufactured by Fuji Pharmaceutical Co., Ltd. was uniformly applied to a thickness of 15 μm on the electrolytic copper plating film and the exposed polyimide resin surface, and dried at 130° C. for 30 minutes.

The substrate obtained by the above treatment was added to hydrazine hydrate for 50 min.
The polyimide resin was dissolved and removed by immersion at °C for 5 minutes. Furthermore, by peeling off the FSR from the substrate, a TAB tape having leads with a lead width of 70 μm and a lead spacing of 60 μm at the inner lead portion was obtained.

The polyimide resin opening shape in the obtained TAB tape was good, and a TAB tape having excellent electrical, mechanical, and heat resistance properties could be manufactured accurately and stably.

[Example 2] The substrate was cleaned using a solution containing 20% by weight of sulfuric acid.
TA was carried out in the same manner as in Example 1 except that it was carried out at 0°C for 2 minutes.
B tape was manufactured.

The polyimide resin opening shape in the obtained TAB tape was good, and a TAB tape having excellent electrical, mechanical, and heat resistance properties could be manufactured accurately and stably.

[Comparative Example 1] A TAB tape was manufactured in the same manner as in Example 1 except that the substrate was not cleaned with sulfuric acid in the process of Example 1.

Regarding the shape of the polyimide resin openings in the obtained TAB tape, over-etching of about 100 μm was observed in the device hole portion and sprocket hole portion.
When this TAB tape is used as an electronic component, it inevitably becomes unreliable.

[Comparative Example 2] The substrate was cleaned using a solution containing 10% by weight of sulfuric acid.
T was carried out in the same manner as in Example 1 except that it was carried out at 0°C for 10 minutes.
AB tape was manufactured.

Regarding the shape of the polyimide resin openings in the obtained TAB tape, over-etching of approximately 70 μm was observed in the device hole portion and sprocket hole portion, and if this TAB tape was used as an electronic component, it would be unreliable. do not have.

[Effects of the Invention] According to the method of the present invention, the adhesion of the etching resist to the surface of the polyimide resin is improved, and as a result, the etching precision of the polyimide resin is improved, and it is excellent electrically, mechanically, and thermally. TAB tape can be manufactured accurately and stably.

・Patent applicant: Sumitomo Metal Mining Co., Ltd.

Claims (1)

[Claims] In a method for dissolving and removing a polyimide resin portion of a copper polyimide substrate obtained by electroless plating on a polyimide resin, followed by electrolytic plating if necessary to form a copper coating, and then heat treatment, the surface of the polyimide resin is A method for etching a polyimide resin, which comprises washing the polyimide resin with sulfuric acid having a concentration of 20% by weight or more, forming an etching resist layer, and etching the portion of the polyimide resin not covered by the etching resist layer.